A block of material of volume 2 X 10\(^{-5}\)m\(^3\) and density 2.5 x 10\(^3\) kgm\(^{-3}\) is suspended from a spring balance with half volume of the block immersed in water. What is the reading of the spring balance? (Density of water =1.0x10\(^3\) kg m\(^{-3}\) g = 10 ms\(^{-2}\)).

  • A 0.10N
  • B 0.25N
  • C 0.30N
  • D 0.40N
  • E 0.50N
waec 1993physics

The correct answer is D. 0.40N

Weight of object = mg

= \(\rho vg\) = 2.5 x 10\(^3\) x 2 x 10\(^{-5}\) x 10 = 0.5N;

Upthrust = weight of displaced fluid = \(\rho_{water} vg\)  

= \(\frac{1.0 \times 10^3 \times 2 \times 10^{-5} \times 10}{2}\) = 0.1N

∴Reading = 0.5 – 0.1 = 0.4N

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